The 2004 Horizon League men's basketball tournament took place at the end of the 2003–04 regular season.
As the highest remaining seed, Milwaukee hosted the championship game.
All Horizon League schools played in the tournament.
Teams were seeded by 2003–04 Horizon League season record, with a tiebreaker system to seed teams with identical conference records.
First round games at campus sites of higher seeds Second round and semifinals hosted by Butler.